Ophthalmic lenses, in particular contact lenses, more particular silicone hydrogel contact lenses, which are intended to be produced economically in large numbers, are preferably produced by the so-called mold or full-mold process. In this process, the lenses are produced in their final shape between two mold halves, so that neither subsequent machining of the surfaces of the lenses nor machining of the edge is necessary. Mold processes are described, for example in WO-A-87/04390, EP-A-0367513 or in U.S. Pat. No. 5,894,002.
In order to produce a contact lens, usually a specific amount of a flowable lens forming material is introduced into the female mold half in a first step. The mold is then closed by putting the male mold half into place. The subsequent polymerization and/or cross-linking of the lens forming material is carried out by means of irradiation with UV light and/or by heating. After the lens if formed, the mold is disassembled and the lens removed. Additional processing steps, such as inspection, extraction, hydration, surface treatment and sterilization may finally be performed on the lens before packaging.
Contact lenses having one or more colorants on the lens for cosmetic purposes are in high demand. These colored contact lenses may enhance the natural beauty of the eye and/or may provide unique patterns on the iris of the wearer. Further, non cosmetic patterns or marks, such as rotation marks, inversion marks, product codes and/or lot numbers may be present on the contact lenses, which are of benefit to wearers, eye-care practitioners and manufacturers. These marks are generally referred to as identification marks.
Ophthalmic lenses, in particular contact lenses use a well-defined geometrical configuration which determines their optical properties. The shape of each lens is characterized by three attributes: (1) the curvature of its two surfaces; (2) the thickness at its center and edges; and (3) its diameter. The two surfaces of a lens can use various geometric configurations, including the following shapes: spherical; cylindrical; toric; plano; aspheric (usually elliptical); and progressive.
For example, the surface of a lens can have a constant radius along its different axes so that the surface is symmetrical, which is known as a spherical surface. The spherical lens surface mirrors the shape of a portion of a sphere in which all meridians have the same radius of curvature. The spherical surface may be either convex or concave.
Alternatively, the surface of the lens can have two axes, each having a different radius of curvature, so that the surface of the lens is asymmetrical. An astigmatic surface is an example of such an asymmetrical surface and is characterized by its two principal meridians having a different radius of curvature from each other. The meridian having the greatest radius of curvature is called the “axis”, and the other meridian having the smaller radius is called the “perpendicular axis”. Astigmatic lens surfaces predominantly include a cylindrical surface and a toric surface. A plano surface and aspheric surface are examples of other lens surfaces used in the art.
For the cylindrical surface, the principal meridians along the axis have an infinite radius of curvature, e. g., flat or straight, and the perpendicular axis has a radius of curvature which is the same as the circular radius of a cylinder. Thus, a concave cylindrical surface is shaped to complementarily receive a cylinder on the surface and a convex surface resembles the exterior surface of such a cylinder.
The tonic surface resembles the lateral surface of a torus, e. g., shaped as the inner tube of a tire. Thus, a torus surface is similar to a cylindrical surface, but the longitudinal axis curves instead of being straight as for a cylindrical surface. The perpendicular axis or meridian on the toric surface has a radius of curvature smaller than the radius of the axis. As with a spherical and a cylindrical surface, a toric surface can be convex by having the shape of the exterior surface of a torus or, alternatively, may be concave by having the shape of the inner surface of a torus.
An astigmatic surface is used for a person with an ocular astigmatism, in which the cornea is elliptical instead of round. The orientation of the elongated portion of an astigmatic cornea varies from person to person. For example, one person may have an axis at five degrees, another at thirty degrees, and another at yet a different orientation.
The axis of the surface of the lens must be oriented to align with the orientation of the elongated portion of the cornea.
Different lens surfaces can be used in combination. Often, the front surface of a lens is spherical and the back surface is spherical, cylindrical, or toric. The front surface can alternatively be a plano surface. The optimum combination of surfaces in a lens is determined by the optical properties, the proposed use, and the appearance of the lens.
In sum, each ophthalmic lens has a unique set of specifications identifying its optical properties. Because a lens formed by molding takes the shape of the molds, the specifications of the lens are determined by the corresponding specifications of the mold, i.e. the two mold halves, as well as by the relative position of the mold halves.
If only lenses with one set of specifications are produced in a particular manufacturing process comprising all the steps from mold to package, there is no need for individual marking of each lens with its set of specifications (e.g. by using an identification mark).
In an automated lens-forming manufacturing process however, usually more than one set of specifications can be produced on one manufacturing line and/or more than one manufacturing line can be utilized to produce lenses in quantity. Often one manufacturing line may produce lenses with one set of specifications. Other lines may produce lenses with another set of specifications.
Generally, lenses with one set of specifications produced on a specific manufacturing line within a defined period of time are called a lot. Usually, each lot is giving a number and said lot number is labeled on all packages of said lot, together with said set of specifications of said lenses.
As each lens has its own set of specifications, at least its package, but preferably the lens itself, must be properly labeled with corresponding specifications before it is delivered to customers. Tracking the specifications of an individual molded lens after its manufacture and verifying its identity is troublesome.
For inventory control of molded lenses an identification mark may be provided on each individual molded lens. The identification mark may include information identifying the lens' optical properties, for example the power of the lens, as well as rotation marks, inversion marks, product codes and/or lot numbers. The identification mark may be visible and readable to human eyes. Preferably, the identification mark is machine readable.
Various methods have been disclosed for bringing cosmetic or non-cosmetic patterns or marks, such as the above described identification marks, onto contact lenses. Said methods include for example printing directly onto the contact lens or printing onto the molding surface of a mold that is then used to make the contact lens.
WO-A-01/24994 discloses a method for labeling an identification mark on a lens for inventory control. The identification mark is placed onto the facing inside surface of a mold by an ink jet printer and is remained there when the lens-forming liquid is cured. Once the lens is formed, but before the demolding of the lens, the identification mark is transferred from the mold to the lens.
WO-A-02/074186 discloses a method for making a colored hydrophilic contact lens, comprising the steps of: coating at least a portion of at least one lens-forming surface of a lens mold with a color coat comprising at least one colorant, and a binder polymer; adding a lens forming composition to the lens mold while maintaining the color coat in position; curing the lens-forming composition to form a coated lens; and subjecting the coated lens to conditions which cause the color coat to adhere to the lens.
WO-A-2005/102675 discloses a method for making a colored silicone hydrogel contact lens, comprising the steps of: (a) applying a color coat to at least a portion of at least one of molding surfaces of a lens mold with an ink comprising at least one colorant and a photo-curable or thermo-curable binder polymer, wherein the mold has a lens-forming cavity between the molding surfaces, wherein the colored coat contains a first surface exposed to the interior of the lens-forming cavity and a second surface in contact with the molding surface; (b) dispensing a lens-forming material into the lens-forming cavity of the mold while maintaining substantially the color coat in position; (c) curing the lens-forming material within the lens-forming cavity to form the contact lens, whereby the colored coat detaches from the molding surface and becomes integral with the body of the contact lens.
An ink can generally be applied to a contact lens or a molding surface of a mold according to any suitable printing technology, such as, for example, pad transfer printing or ink jet printing. It is understood that other types of printing technologies could also be used to print on a lens or to print on a mold.
For ink jet applications, the ink usually has one or more of the following characteristics: a viscosity lower than 50 m Pa·s, preferably lower than 15 m Pa·s; most preferably below 15 m Pa·s; a surface tension of from 20 mN/m to 60 mN/m; a particle size of less than 5 μm, preferably lower than 1 μm; most preferably below 0.5 μm; prolonged stability (i.e., stable for at least 4 hours, preferably at least 8 hours, more preferably at least 24 hours); an appropriate color level (i.e. visible by eye); uniform drop formation and jet stability; good adhesion to contact lenses; good transfer from a mold to a contact lens made in the mold; and stability of the ink in the ink jet nozzles (i.e. minimal drying or crusting effects).
The methods of the prior art however usually have the disadvantage, that an ink drop applied through pad transfer printing, but in particular applied through ink jet printing, usually is moved from its original position on the surface of the mold half and/or is deformed in its original position through the forces exerted by the flowing lens forming material upon closing of the mold. Accordingly, prior art methods either suggest to print directly onto the formed lens or suggest pre-curing the printed ink in the mold before adding the lens forming material. Said methods however add complexity to the process and increase the manufacturing costs.
Accordingly, there is a need to provide an improved method allowing for an industrial scale manufacturing process of molded articles with limited complexity (i.e. less handling steps) and at low cost.
It is an object of the present invention to provide an improved method for making a colored contact lens, in particular for making a contact lens comprising an identification mark on the lens.